With temperature 30°C and dew point 20°C, estimate the cloud base in feet AGL.

With temperature 30°C and dew point 20°C, estimate the cloud base in feet AGL.

• A. 3,000 feet
• B. 5,000 feet
• C. 4,500 feet
• D. 4,000 feet

Answer: (D)

Cloud base height can be estimated from how far the air must rise to cool to the dew point. The dew point tells us the temperature at which air becomes saturated; the larger the difference between the surface temperature and the dew point, the higher the cloud base will be. A common quick rule of thumb uses the difference in Celsius and yields cloud base in feet: about 400 feet per degree Celsius of spread. Here, the surface temperature is 30°C and the dew point is 20°C, so the difference is 10°C. Multiply by 400 and you get roughly 4,000 feet AGL. So the cloud base is about 4,000 feet above the ground. This is an approximate estimate and can vary with actual atmospheric conditions, but it aligns with the typical rule used for a quick calculation.

Cloud base height can be estimated from how far the air must rise to cool to the dew point. The dew point tells us the temperature at which air becomes saturated; the larger the difference between the surface temperature and the dew point, the higher the cloud base will be. A common quick rule of thumb uses the difference in Celsius and yields cloud base in feet: about 400 feet per degree Celsius of spread.

Here, the surface temperature is 30°C and the dew point is 20°C, so the difference is 10°C. Multiply by 400 and you get roughly 4,000 feet AGL. So the cloud base is about 4,000 feet above the ground. This is an approximate estimate and can vary with actual atmospheric conditions, but it aligns with the typical rule used for a quick calculation.